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Campylobacter jejuni and Campylobacter coli infections are the leading cause of foodborne gastroenteritis in high‐income countries. Campylobacter colonizes a variety of warm‐blooded hosts that are reservoirs for human campylobacteriosis. The proportions of Australian cases attributable to different animal reservoirs are unknown but can be estimated by comparing the frequency of different sequence types in cases and reservoirs. Campylobacter isolates were obtained from notified human cases and raw meat and offal from the major livestock in Australia between 2017 and 2019. Isolates were typed using multi‐locus sequence genotyping. We used Bayesian source attribution models including the asymmetric island model, the modified Hald model, and their generalizations. Some models included an "unsampled" source to estimate the proportion of cases attributable to wild, feral, or domestic animal reservoirs not sampled in our study. Model fits were compared using the Watanabe–Akaike information criterion. We included 612 food and 710 human case isolates. The best fitting models attributed >80% of Campylobacter cases to chickens, with a greater proportion of C. coli (>84%) than C. jejuni (>77%). The best fitting model that included an unsampled source attributed 14% (95% credible interval [CrI]: 0.3%–32%) to the unsampled source and only 2% to ruminants (95% CrI: 0.3%–12%) and 2% to pigs (95% CrI: 0.2%–11%) The best fitting model that did not include an unsampled source attributed 12% to ruminants (95% CrI: 1.3%–33%) and 6% to pigs (95% CrI: 1.1%–19%). Chickens were the leading source of human Campylobacter infections in Australia in 2017–2019 and should remain the focus of interventions to reduce burden. [ABSTRACT FROM AUTHOR]

We used genomic and epidemiological data to assess and compare the population structure and origins of Campylobacter, a major foodborne pathogen, in two neighbouring countries with strong trade and cultural links, similar poultry production systems and frequent movement of people and food products. The most common sequence types (STs) differed between Australia and New Zealand, with many unique to each country. Over half of all STs were represented by a single isolate. Multidrug-resistant (MDR) genotypes were detected in 0.8% of all samples, with no MDR isolates detected in poultry. Quinolone and tetracycline resistant ST6964 was prevalent in New Zealand (10.6% of C. jejuni ). Closely related isolates suggested some similar food sources or contacts. We have shown that there is little genetic overlap in human and poultry STs of Campylobacter between the countries, which highlights that this common foodborne pathogen has domestic origins in Australia and New Zealand.

Campylobacter is a globally important pathogen with well-studied risk factors, but the burden of risk factors has not been quantified. We quantified the cost of illness attributable to specific domestic risk factors for C. jejuni and C. coli in Australia. We used data from a 2018-2019 case-control study to estimate odds ratios and attributable fractions for risk factors. We used data on national incidence, hospitalization, and premature mortality to quantify burden. We then applied costs related to healthcare utilization, pain and suffering, premature mortality, and lost productivity to each risk factor. In Australia, C. jejuni caused 83.0% of campylobacteriosis infections and chicken consumption resulted in the highest attributable fraction (30.0%), costing approximately US$110 million annually. The excess burden of campylobacteriosis associated with the use of proton-pump inhibitors (PPIs) was US$45 million, with almost half these costs due to disease in adults over 65 years of age. Contact with young dogs (US$30 million) and chicken feces (US$10 million) also contributed to costs and burden. Campylobacteriosis is a significant cost to Australia, particularly because of lost productivity. Effective cross-sectoral interventions to improve chicken meat safety and reduce inappropriate use of PPIs might have substantial economic and human benefits.

Campylobacter spp. are a common cause of bacterial gastroenteritis in Australia, primarily acquired from contaminated meat. We investigated the relationship between genomic virulence characteristics and the severity of campylobacteriosis, hospitalisation, and other host factors.We recruited 571 campylobacteriosis cases from three Australian states and territories (2018-2019). We collected demographic, health status, risk factors, and self-reported disease data. We whole genome sequenced 422 C . jejuni and 84 C . coli case isolates along with 616 retail meat isolates. We classified case illness severity using a modified Vesikari scoring system, performed phylogenomic analysis, and explored risk factors for hospitalisation and illness severity.On average, cases experienced a 7.5 day diarrhoeal illness with additional symptoms including stomach cramps (87.1 %), fever (75.6 %), and nausea (72.0 %). Cases aged ≥75 years had milder symptoms, lower Vesikari scores, and higher odds of hospitalisation compared to younger cases. Chronic gastrointestinal illnesses also increased odds of hospitalisation. We observed significant diversity among isolates, with 65 C . jejuni and 21 C . coli sequence types. Antimicrobial resistance genes were detected in 20.4 % of isolates, but multidrug resistance was rare (0.04 %). Key virulence genes such as cdtABC ( C. jejuni ) and cadF were prevalent (>90 % presence) but did not correlate with disease severity or hospitalisation. However, certain genes (e.g. fliK , Cj1136 , and Cj1138 ) appeared to distinguish human C. jejuni cases from food source isolates.Campylobacteriosis generally presents similarly across cases, though some are more severe. Genotypic virulence factors identified in the literature to-date do not predict disease severity but may differentiate human C. jejuni cases from food source isolates. Host factors like age and comorbidities have a greater influence on health outcomes than virulence factors.

Campylobacter jejuni and Campylobacter coli infections are the leading cause of foodborne gastroenteritis in high-income countries. Campylobacter colonizes a variety of warm-blooded hosts that are reservoirs for human campylobacteriosis. The proportions of Australian cases attributable to different animal reservoirs are unknown but can be estimated by comparing the frequency of different sequence types in cases and reservoirs. Campylobacter isolates were obtained from notified human cases and raw meat and offal from the major livestock in Australia between 2017 and 2019. Isolates were typed using multi-locus sequence genotyping. We used Bayesian source attribution models including the asymmetric island model, the modified Hald model, and their generalizations. Some models included an "unsampled" source to estimate the proportion of cases attributable to wild, feral, or domestic animal reservoirs not sampled in our study. Model fits were compared using the Watanabe-Akaike information criterion. We included 612 food and 710 human case isolates. The best fitting models attributed >80% of Campylobacter cases to chickens, with a greater proportion of C. coli (>84%) than C. jejuni (>77%). The best fitting model that included an unsampled source attributed 14% (95% credible interval [CrI]: 0.3%-32%) to the unsampled source and only 2% to ruminants (95% CrI: 0.3%-12%) and 2% to pigs (95% CrI: 0.2%-11%) The best fitting model that did not include an unsampled source attributed 12% to ruminants (95% CrI: 1.3%-33%) and 6% to pigs (95% CrI: 1.1%-19%). Chickens were the leading source of human Campylobacter infections in Australia in 2017-2019 and should remain the focus of interventions to reduce burden., (© 2023 The Authors. Risk Analysis published by Wiley Periodicals LLC on behalf of Society for Risk Analysis.)